In general, the design and manufacture of a tire includes consideration of multiple factors such as e.g., tread wear, rolling resistance, traction, noise generation, and numerous others as well. Problems are encountered in attempting to optimize such factors because, conventionally, improvement of one factor may have a deleterious impact on one or more other factors. As such, typically a balance or compromise is selected.
For example, one common problem confronted in tire design and manufacture is how to maintain traction performance in soft ground conditions like e.g., mud and snow, over the wear life of the tread—particularly at later stages of wear life. Prior approaches have included treads having ribs that are separated by circumferentially extending grooves with the ribs divided into a plurality of segments by lateral incisions sometimes referred to as lamelles or sipes. Such designs can enhance tread life and/or rolling resistance performance while also providing for traction performance in soft ground conditions provided that the depth of the lamelles is relatively high. Unfortunately, however, as the tread wears and the depth of the lamelles is reduced, traction performance in soft ground conditions is reduced because the segments lose the ability to develop over pressure on the edges.
In an effort to compensate for the reduction in soft ground traction performance, the cross-sectional area of the lamelles in the contact patch can be increased by increasing the width of the lamelles along the circumferential direction. For example, a layered tread can be provided where the first layer contains relatively narrow lamelles in the early stages of tread wear that give way to relatively wider lateral grooves in a second layer that is revealed in later stages of tread wear. In the early stages of tread wear in the first layer, such lateral grooves exist as channels that are extended completely across the lateral width of the rib or tread block so as to open to circumferential grooves located on both lateral sides of the rib or tread block. As the tread wears down to the second layer to convert the channels into exposed lateral grooves, the width (along the circumferential direction) of such lateral grooves can enhance traction in soft ground such as mud or snow. However, despite the benefits of such design, certain challenges still remain.
For example, during the early stages of the wear life of the tread in the first layer, the lateral channels are positioned radially inward of tread rubber in the first layer. As such, the channels are compressed as the tire rolls through the contact patch, which causes the channels to pump air into the circumferential grooves on either side of the rib or tread block. This excitation of the air can lead to increase acoustical effects such as drive by or coast by noise. In addition, the lateral channels also induce discontinuities in the transmission of contact stresses from the ground to the casing through the tread, which causes higher vibratory excitation of the tire leading to additional acoustical effects such as coast by noise.
Accordingly, in view of the problems in the art including those set forth above, there is a need for a tire tread that can have improved traction performance on soft ground with a decrease in acoustical effects such as coast by noise. There is also a need for such a tire tread that can also have desirable levels of rolling resistance and/or wear life.